Our research deals principally with lipids of virulent tubercle bacilli. Cord factor and the mycobacterial sulfatides are two classes of trehalose-containing glycolipids from M. tuberculosis which are implicated in virulence and in the pathogenesis of the disease. Both substances also have antitumor activity in the line 10 strain-2 guinea pig system. A part of our studies involves synthesis of pseudo cord factors, principally based upon "trehalose dicarboxylic acid" as inexpensive substitutes for the natural product, potentially useful in tumor immunotherapy. The influence of structural changes on biological activity provides information on structure-functional relationships. The sulfatides (and other polyanionic agents as well) prevent phagosome-lysome fusion in cultured macrophages. The former are therefore probably functional in promoting the intracellular survival of M. tuberculosis. Our current studies concern the influence of macrophage activation on abrogating the block to fusion; and on bactericidal mechanisms in macrophages. In an extension of earlier work correlating specific lipids of M. tuberculosis with phage type, characteristic lipids of thirty aberrant strains were quantitated; a new Attenuation Indicator (AI) lipid was recognized and it is believed to be a partially acylated precursor of the original AI lipid. It will be recovered from mass culture of an appropriate strain and its structure elucidated.